I. Field of the Invention
This invention relates to molding machines, more particularly, to ejector mechanisms commonly used in molding machines. The invention is directed particularly to setting travel limits for ejector mechanisms.
II. Description of Related Art
In molding machines, plastically deformable material to be molded is formed in cavities defined by mating mold sections and allowed to cure to a state wherein the material will not unacceptably deform upon removal from the mold cavity. The cured material defines molded articles that are removed from the machine upon separation of the mating mold sections. However, as it is common that articles will adhere to one of the mold sections, it is typical to provide ejector pins communicating with the mold cavity and linked to movable members in the mold assembly comprising the mating mold sections. Motion of the ejector pins is effective to dislodge molded articles from the mold section, assuring their complete removal. The movable members are typically translatable and include links to the ejector pins to move them between retracted positions whereat their free ends are flush with mold cavity surfaces and forward positions whereat the free ends protrude into the mold cavity.
From U.S. Pat. No. 5,639,486 it is known to provide for calibration of a control of an ejector mechanism to establish a position value corresponding to or derived from an ejector retract travel extreme. In accordance with this patent, the ejector mechanism is controlled to retract to the travel extreme where motion is mechanically restrained and record a representation of position corresponding to the travel extreme. To prevent overloading the ejector mechanism, the retraction is stopped on detection of cessation of motion by a mechanical restraint (xe2x80x9cstopperxe2x80x9d). The ejector may be advance away from the stopper a predetermined distance xe2x80x9cLxe2x80x9d to define a xe2x80x9ccalibration completion positionxe2x80x9d.
As mold cavity depths vary according to the articles being produced, the translation of movable members required to dislodge articles varies accordingly. Although the calibration technique known from U.S. Pat. No. 5,639,486 is suitable for establishing a coordinate value associated with a retract position, known procedures for establishing stroke length for ejector mechanisms require data entry by a user having access to information concerning a mold assembly. Consequently, errors in setting of values for control of ejectors can result, and such errors may cause malfunctions of ejector mechanisms, triggering alarms and/or damaging machine or mold elements. Consequently, there is a need for improved methods for setting ejector mechanism stroke lengths that overcome the deficiencies of known methods.
It is an object of the present invention to provide improved methods and apparatus for setting program controlled stroke length of ejector mechanisms for molding machines.
It is a further object of the present invention to provide an improved method for setting stroke length of an ejector mechanism of a molding machine wherein coordinate values of advance and retract end points are determined and recorded without operator intervention.
Further objects and advantages of the invention shall be made apparent from the accompanying drawings and the following description thereof.
In accordance with the aforesaid objects the present invention provides a method for setting a program controlled stroke length of an ejector mechanism of a molding machine. The ejector mechanism imparts translation to movable members of a mold assembly, the movable members being linked to ejector pins communicating with a mold cavity defined by mating mold sections. A procedure is performed under program control to effect definition of ejector travel limit position information. To limit forces generated during execution of the limit setting procedure, the procedure causes setting of an ejector actuator control parameter to limit useful force produced by the ejector actuator. The procedure then causes the ejector mechanism to be driven to advance the movable members to the extremes of their travel range, in each direction, motion being ceased as a result of physical restraint. Travel limit position information is defined in response to detection of restraint of motion at the travel range extremes. The definition of travel limit positions for both forward and rearward travel limits establishes an ejector stroke length adapted to the peculiarities of the mold assembly.